The present invention relates to readable and/or writable memory devices, such as radio frequency memory tags.
A variety of methods exist for tracking and providing information about items. For example, inventory items in stores typically bear printed labels providing information such as serial numbers, price, weight, and size. Some labels include machine-readable symbols, such as bar code symbols, which may be selected from a variety of symbologies. These labels contain a limited amount of information due to space constraints. Updating the information on these labels typically requires the printing of a new label to replace the old label.
Memory devices such as radio frequency (xe2x80x9cRFxe2x80x9d) tags provide an alternative method of tracking and providing information about items. Memory devices permit large amounts of data to be associated with an object or item. Memory devices typically include a memory and logic in the form of an integrated circuit (xe2x80x9cICxe2x80x9d) and means for transmitting data to and from the memory. For example, an RF tag typically includes a memory, an RF transmitting section, an RF receiving section, an antenna, and logic for controlling the memory, the RF transmitting section and the RF receiving section. RF tags are generally formed on a substrate and may include, for example, analog RF circuits and digital logic and memory circuits. The RF tags may also include a number of discrete components, such as capacitors and diodes where such is advantageous.
The RF tags may be either passive or active devices. Active devices are self-powered, by a battery, for example. Passive devices do not contain a power source, but derive their energy from the RF signal used to interrogate the RF tag. Passive RF tags usually include an analog circuit which detects and decodes the interrogating RF signal and which provides power from the RF field to a digital circuit in the tag. The digital circuit generally executes all of the functions performed by the RF tag, such as retrieving stored data from memory and modulating the RF signal to transmit the retrieved data. In addition to retrieving and transmitting data previously stored in the memory, the RF tag may permit new or additional information to be stored into the RF tag""s memory or may permit the RF tag to manipulate data or perform some additional functions.
A significant drawback of memory devices such as RF tags is the inability to associate a specific memory device, or item to which it is attached, with a given data signal. For example, where a number of longer range RF tags (e.g., range greater than approximately 6 inches) are in relatively close proximity to one another, a reader will receive data from all of the RF tags in either a defined sequence or a random sequence. However, the reader is unable to associate the received data with any particular RF tag. So, while a user may determine that a particular item is present among a number of items or containers, the user is unable to specifically identify which one of the items or containers the data describes.
Attempts have been made to overcome this problem. For example, one cost-effective means of associating data with a particular item is to physically move each item out of range of the reader until the desired item is identified. Another attempt includes the use of triangulation. However triangulation has accuracy limitations and requires multiple pieces of equipment or multiple sampling of data at different locations.
In one aspect of the invention, a system for storing and retrieving data comprises a memory device such as a radio frequency tag having a memory for storing the data, a first identifier stored in the memory of the memory device, and a machine-readable symbol associated with the memory device, where at least a portion of the machine-readable symbol encodes a second identifier logically associable with the first identifier. The machine-readable symbol may, for example, be printed on the memory device, or may be carried by a container that also carries the memory device. The data stored in the memory device may include data related to the container or items carried by the container.
In another aspect of the invention, at least a portion of a machine-readable symbol includes a flag, the flag being logically associated with the existence of a memory device such as an RF tag corresponding to the machine-readable symbol. The flag is set to a first value when an RF tag corresponding to the machine-readable symbol exists, and to a second value when an RF tag does not exist. Thus, a reader reading the machine-readable symbol is able to determine whether an RF tag exists and may control an RF portion of the reader appropriately.
Similarly, in another aspect of the invention, a machine-readable symbology includes a number of symbol characters, including a flag character that indicates that at least one memory device corresponding to the machine-readable symbol exists.
In another aspect of the invention, a method of conserving power in a reader includes operating a symbol reading portion of the reader to read a symbol, determining whether a memory device is associated with the symbol from the data encoded in the read symbol, and operating a memory device reader portion of the reader if a memory device is associated with the symbol.
In yet another aspect of the invention, a method of associating a machine-readable symbol with data stored in one of a number of memory devices includes reading the machine-readable symbol to obtain a symbol identifier, and successively reading each of a number of memory devices to obtain a memory device identifier and comparing the memory device identifier and the symbol identifier, until a memory device is read that has a memory device identifier that corresponds to the symbol identifier.
In a further aspect of the invention, a method of associating a machine-readable symbol with data stored in one of a number of memory devices includes successively reading each of the number of memory devices to obtain a memory device identifier for each of the number of memory devices, reading the machine-readable symbol to obtain a symbol identifier, and matching the symbol identifier to the memory device identifier of one of the number of memory devices.